Molecular weight regulation in polymerization of vinylidene monomers using a phosphite regulator



United States Patent 3,222,335 MOLECULAR WEIGHT REGULATION IN POLYM- ERIZATION 0F VINYLIDENE MONOMERS USING A PHOSPHITE REGULATOR Richard Delacretaz, Springfield, Mass., assignor to Monsanto Company, a corporation of Delaware No Drawing. Filed Nov. 3, 1961, Ser. No. 149,865 7 Claims. (Cl. 260-855) This invention relates to the polymerization of a free radical-polynlerizable material including a polar monomer and more particularly relates to a method of regulating the molecular weights of polymers prepared by polymerizing such a free radical-polymerizable material in the absence of an organic diluent.

The tendency of certain free radical-polymerizable materials to polymerize to very high molecular Weight polymers under normal polymerization conditions is already Well known. These very high molecular weight polymers have the disadvantage of being difiiculty processable, i.e., unable to be processed without the use of special processing equipment except at temperatures so high as to have a detrimental effect on the strength and color of the processed polymers.

Various techniques have been proposed for regulating the molecular weights of such polymers so as to make them more easily processable. One of these techniques is to conduct the polymerization in an organic diluent. This technique is elfective as a means of lowering molecular weight, but it has the disadvantages of increased cost and inconvenience of separating the polymer from the organic diluent. Other proposed techniques avoid the disadvantages of solvent polymerization but have unfortunate disadvantages of their own, e.g., raising the polymerization temperature increases the danger of a runaway polymerization, and using a mercaptan as a chain transfer agent contributes a very unpleasant odor to the polymers.

An object of the invention is to provide more easily processed polymers of the type prepared by polymerizing a free radical-polymerizable material including a polar monomer.

Another object is to provide a novel process for regulating the molecular weights of such polymers without employing an organic diluent in the polymerization reaction mixture.

These and other objects are attained by conducting the polymerization of a free radical-polymerizable material including a polar monomer, as hereinafter more completely described, in the absence of an organic diluent and in the presence of 0.05% based on the weight of the free radical-polymerizable material, of a molecular weight regulator which corresponds to the formula:

POH R O/ wherein R represents a member of the group consisting of hydrogen, an alkyl radical, and an aryl radical and R represents a member of the group consisting of an alkyl radical and an aryl radical.

The following examples are given to illustrate the invention. Unless otherwise specified, quantities are mentioned on a weight basis, and polymer properties are determined under the same conditions in each part of any one example.

EXAMPLE I.POLYVINYL CHLORIDE Part A Charge 100 parts of purified vinyl chloride monomer, 150 parts of water, 0.15 part of lauroyl peroxide, and 0.5 part of a water-soluble acrylic acid-Z-ethylhexyl acrylate "Ice (:10) copolymer to a suitable reaction vessel. Seal the vessel and tumble it in a constant temperature bath at 50 C. for 15 hours. The polymeric product has a specific viscosity of 0.540, measured as a solution of 0.25% of the polymer in cyclohexanone.

Part B Repeat Part A except for including 0.5 part of ethyl acid phosphite in the charge to the reaction vessel. The polymeric product has a specific viscosity of 0.46.

Part C Repeat Part A except for including 0.5 part of butyl acid phosphite in the charge to the reaction vessel. The polymeric product has a specific viscosity of 0.44.

Part D Repeat Part A except for including 0.5 part of 2-ethylhexyl acid phosphite in the charge to the reaction vessel.-

The polymeric product has a specific viscosity of 0.47.

EXAMPLE II.--POLY METHYL METHACRYLATE Part A Charge parts of methyl methacrylate, 0.5 part of benzoyl peroxide, and 0.02 part of t-butyl peracetate to a suitable reaction vessel. Purge with nitrogen, seal the vessel, and heat at 80 C. for 5 hours and then at C. for 5 hours. Purify the product by dissolving it in methyl ethyl ketone and then precipitating it in methanol. The polymer product has a specific viscosity of 0.118, measured as a solution of 0.1% of the polymer in dimethylformamide.

Part B Repeat Part A except for including 0.2 part of butyl acid phosphite in the charge to the reaction vessel. The polymeric product has a specific viscosity of 0.104.

Part C Repeat Part A except for including 0.2 part of ethyl acid phosphite in the charge to the reaction vessel. The polymeric product has a specific viscosity of 0.102.

Part D Repeat Part A except for including 0.2 part of 2-ethylhexyl acid phosphite in the charge to the reaction vessel. The polymeric product has a specific viscosity of 0.091.

EXAMPLE III.STYRENEACRYLONITRILE COPOLYMER Part A Charge 70 parts of styrene, 30 parts of acrylonitrile, 0.05 part of dicumyl peroxide, and 0.1 part of di-t-butylp-cresol to a suitable reaction vessel. Purge with nitrogen, seal the vessel, and heat at 120 C. for 4 hours and then at C. for 4 hours. The polymeric product has a specific viscosity of 0.200, measured as a solution of 0.1% of the polymer in dimethylformamide.

PartB Repeat Part A except for including 0.5 part of ethyl acid phosphite in the charge to the reaction vessel. The polymeric product has a specific viscosity of 0.173.

Part C Repeat Part A except for including 0.5 part of butyl acid phosphite in the charge to the reaction vessel. The polymeric product has a specific viscosity of 0.163.

Part D Repeat Part A except for including 0.5 part of Z-ethylhexyl acid phosphite in the charge to the reaction vessel. The polymeric product has a specific viscosity of 0.172.

The invention is a method of regulating the molecular weights of polymers prepared from a free radical-polymerizable material including a polar monomer without employing an organic diluent. The molecular weight regulation is achieved by conducting the polymerization of the free radical-polymerizable material in the presence of a minor amount of a molecular weight regulator which corresponds to the formula:

POH RO wherein R represents a member of the group consisting of hydrogen, an alkyl radical, and an aryl radical and R represents a member of the group consisting of an alkyl radical and an aryl radical.

Exemplary of utilizable molecular weight regulators are the methyl, ethyl, propyl, butyl, hexyl, octyl, nonyl, decyl, and phenyl acid and diacid phosphites, etc., and mixtures thereof.

The amount of molecular weight regulator employed in the practice of the invention is in the range of 0.05 usually 0.1-3%, based on the weight of the free radicalpolymeriza'ble material. The acid and diacid phosphites are ineffective as molecular weight regulators at concentrations lower than 0.05%. Concentrations higher than 5% are usually undesirable, either because the higher concentration causes too great a reduction of the molecular weight of the polymer or because the amount of molecular weight regulator which becomes chemicallycombined into the polymer is large enough to noticeably affect polymer properties other than the properties attributable to molecular weight. A particular advantage of the molecular weight regulators of the invention is their ability to act as molecular weight regulators at such low concentrations that substantially their only contribution to the properties of the polymers prepared in their presence is an improvement in processability.

The free radical-polymerizable materials which are polymerized in the presence of the molecular weight regulators of the invention are materials including a polar monomer, Le, a monomer which has a dipole moment of at least 1.0 Debye unit. Particularly suitable materials are:

(1) Polar vinylidene monomers, such as acrylonitrile, methacrylonitrile, vinyl chloride, an alkyl aorylate (e.g., methyl acrylate, ethyl acrylate, butyl acrylate, Z-ethylhexyl acrylate, dodecyl acrylate, etc.), an alkyl methacrylate (e.g., methyl methacrylate, butyl methacrylate, etc.) and mixtures thereof,

(2) Mixtures of such polar vinylidene monomers with copolymerizable monomers, such as dialkyl maleates, dialkyl fumarates, acrylic acid, methacrylic acid, conjugated dienes (e.g., butadiene), monovinylidene aromatic hydrocarbons (e.g., styrene, alphamethylstyrene, alphaethylstyrene, o-, m-, and p-methylstyrenes, 0-, m-, and p-methyLaIpha-methylstyrenes, p-isopropylstyrene, ar-dibutylstyrenes, vinyl naphthalene, etc.), and

(3) Mixtures of non-polar vinylidene monomers with one or more copolymerizable polar compounds other than the polar monomers mentioned above, such as monoor dialkyl maleates or fumarates, maleic anhydride, acrylic acid, methacrylic acid, etc.

A polar monomer should comprise at least of the weight of the free radical-polymerizable material. According to one of the preferred embodiments of the invention, the free radical-polymerizable material consists of 10-90% by Weight of one or more monovinylidene aromatic hydrocarbons and 90-10% by weight of acrylonitrile and/or methacrylonitr-ile.

The polymerization of the free radical-polymerizable material in the presence of a molecular weight regulator of the invention is conducted in the absence of an organic diluent. Polymerization may be accomplished by any of the mass, suspension, or emulsion polymerization techniques conventionally employed for the polymeriz..- tion of such materials, usually at temperatures in the range of 30200 C. at atmospheric or super-atmospheric pressure. The reaction mixture should contain a free radical polymerization initiator, such as a peroxy or azo compound, and any ingredient required by the particular polymerization technique employed, e.g., water, an emulsifying agent, a suspending agent, etc. Optional ingredients, such as antioxidants. plasticizers, etc., can also be included in the reaction mixture if desired.

A preferred embodiment of the invention is the use of the molecular weight regulators in polymerization reactions which are conducted in an aqueous medium. Ordinarily in such reactions the weight ratio of water to free radical-polymerizable material is in the range of 9:1 to 2:3. The emulsifying agent, when employed, can be of the anionic, cationic, or nonionic type; the suspending agent, when employed, can be inorganic or organic.

It is within the scope of the invention to conduct the polymerization in the presence of a preformed polymer, e.g., polybutadiene, a rubbery butadiene-styrene copolymer, or the like, to graft polymeric chains of the free radical-polymerizable material onto th preformed polymer backbone. The molecular weight regulator serves to shorten the chains grafted onto the polymer backbone as well as to lower the molecular weight of any co-formed, ungrafted polymer of the free radical polymerizable material.

The products of the invention are polymers which contain a minor amount of chemically-combined molecular weight regulator and have lower molecular weights than the corresponding polymers prepared in the absence of the molecular Weight regulators. Because of their lower molecular Weights, they are more easily processable and can be processed, e.g., extruded, molded, etc., in conventional processing equipment without requiring the use of extreme temperatures which would have a detrimental eifect on the strength and color of the products.

The invention is particularly advantageous in that it accomplishes molecular weight regulation without the aid of organic diluents, malodorous mercaptans, or reactive materials which would have to be used in such large amounts as to have a noticeable effect on other polymer properties as well as on processability.

It is obvious that many variations can be made in the products and processes set forth above without departing from the spirit and scope of this invention.

What is claimed is:

1. In a process for polymerizing a free radical-polymerizable material of the group consisting of (a) a polar vinylidene monomer of the group consisting of acrylonitrile, methacrylonitrile, vinyl chloride, an alkyl acrylate, an alkyl methacrylate, and mixtures thereof, (b) mixtures of said polar vinylidene monomer with a copolymerizable monomer of the group consisting of a dialkyl maleate, a dialkyl fumarate, acrylic acid, methacrylic acid, a conju gated diene, a monovinylidene aromatic hydrocarbon, and mixtures thereof, and (c) mixtures of a non-polar vinylidene monomer with a copolymerizable polar monomer of the group consisting of a monoalkyl maleate, a monoalkyl fumarate, a dialkyl maleate, a dialkyl fumarate, maleic anhydride, acrylic acid, methacrylic acid, and mixtures thereof in the presence of a free radical polymerization initiator, the improvement which comprises conducting the polymerization in the presence of 0.05-5 based on the weight of the free radical-polymerizable material, of a molecular weight regulator which corresponds to the formula:

wherein R represents a member of the group consisting of an alkyl radical and an aryl radical. I

2. A process as in claim 1 wherein the free radical- 5 polymerizable material consists of 10-90% by weight of a monovinylidene aromatic hydrocarbon and 90-10% by weight of acrylonitrile.

3. A process as in claim 2 wherein the free radicalpolymerizable material consists of 10-90% by Weight of styrene and 9010% :by weight of acrylonitrile.

4. A process as in claim 1 wherein the polymerization is conducted in an aqueous medium.

5. A process as in claim 1 wherein the molecular weight regulator is ethyl acid phosphite.

6. A process as in claim 1 wherein the molecular weight regulator is butyl acid phosphite.

7. A process as in claim 1 wherein the molecular Weight regulator is 2-ethylhexyl acid phosphite.

References Cited by the Examiner UNITED STATES PATENTS 2,543,636 2/1951 Loritsch 26088.7 2,629,711 2/1953 Stanin et a1. 260-32.6 3,110,702 11/1963 Delacretaz 26086.7

JOSEPH L. SCHOFER, Primary Examiner.

P. E. MANGAN, LEON I. BERCOVITZ, JAMES. A.

SEIDLECK, Examiners. 

1. IN A PROCESS FOR POLYMERIZING A FREE RADICAL-POLYMERIZABLE MATERIAL OF THE GROUP CONSITING OF (A) A POLAR VINYLIDENE MONOMER OF THE GROUP CONSISTING OF ACRYLONITRILE, METHACRYLONITRILE, VINYL CHLORIDE, AN ALKYL ACRYLATE, ANALKYL METHACRYLATE, AND MIXTURES THEREOF, (B) MIXTURES OF SAID POLAR VINYLIDENE MONOMER WITH A COPOLYMERIZABLE MONOMER OF THE GROUP CONSISTING OF A DIALKYL MALEATE, A DIALKYL FUMARATE, ACRYLIC ACID, METHACRYLIC ACID, A CONJUGATED DIENE, A MONOVINYLIDENE AROMATIC HYDROCARBON, AND MIXTURES THEREOF, AND (C) MIXTURES OF A NON-POLAR VINYLIDENE MONOMER WITH A COPOLYMERIZABLE POLAR MONOMER OF THE GROUP CONSISTING OF A MONOALKYL MALEATE, A MONOALKYL FUMARATE, A DIALKYL MALEATE, A DIALKYL FUMARATE, MALEIC ANHYDRIDE, ACRYLIC ACID, METHACRYLIC ACID, AND MIXTURES THEREOF IN THE PRESENCE OF A FREE RADICAL POLYMERIZATION INITIATOR, THE IMPROVEMENT WHICH COMPRISES CONDUCTING THE POLYMERIZATION IN THE PRESENCE OF 0.05-5%, BASED ON THE WEIGHT OF THE FREE RADICAL-POLYMERIZABLE MATERIAL, OF A MOLECULAR WEIGHT REGULATOR WHICH CORRESPONDS TO THE FORMULA: 